Generally, a weight sensing device for vehicles is designed to provide data about the weight of a passenger to an airbag controller, which determines an explosion range of an airbag by taking into consideration a distance between an installed position of the airbag and the passenger, a position and weight of the passenger, and the like.
A conventional weight sensing device for vehicles is configured in such a manner that a metal member, to which a typical strain gauge is attached, is installed underneath a passenger seat, to measure a strain caused by a vertical load of a passenger. However, the strain gauge is adapted to measure a strain due to moment and lateral load caused upon sudden braking or a variation in traveling conditions of a vehicle, as well as stain caused by the vertical load, and therefore, has difficult accurately measuring only a weight of the passenger.
For this reason, recently, a weight sensing device for vehicles has been proposed, wherein a semiconductor strain gauge, which has a high sensitivity to even a slight strain, is attached to a diaphragm which serves to compensate for moment or lateral load. Now, the conventional weight sensing device for vehicles will be described in more detail.
The conventional weight sensing device for vehicles, to which the semiconductor strain gauge is attached, as shown in FIG. 1, includes an upper cover 110 fastened to a seat frame 100, and a lower support 120 fastened to a slide rail 200 and adapted to support a center diaphragm 121, the upper cover 110 and lower support 120 being arranged opposite each other on the same vertical axis. If a vertical load of a passenger is applied to the weight sensing device, a hollow press portion 111 formed at a tip end of the upper cover 110 presses a flange portion 122 of the lower support 120 formed around an outer periphery of the diaphragm 121, causing deformation of the diaphragm 121 and allowing a semiconductor strain gauge 130 attached to the diaphragm 121 to measure a weight of the passenger.
However, in the above-described conventional weight sensing device for vehicles, wherein the vertical load of the passenger is input and output on the same axis and the weight sensing device is divided into two bodies including the upper cover 110 and lower support 120, acquisition of an accurate measured value is difficult if axes of the upper cover 110 and lower support 120 are inconsistent with each other. In particular, the conventional weight sensing device must be designed to a high entire height and has difficulty in compatible use with all kinds of vehicles